The present invention concerns a satellite communication system for broadcasting audiovisual programs and multimedia data.
French Patent No. 2 723 279 describes a communication system of the above type comprising a plurality of transmitters, each of which transmits a transmit signal carrying a television program, and a satellite comprising a multiplexer combining said transmit signals to form a transmit multiplex that is broadcast to users"" receivers on a downlink frequency channel.
To be more precise, a transmit signal comprises an audio signal, a video signal and optionally data. The audio and video signals can be encoded to the MPEG-2 (Moving Picture Expert Group No. 2) standard, which is well known in the art (ISO/IEC Standard 13 818). The transmit signal, structured into transport packets, is transmitted in accordance with the DVB-S (Digital Video Broadcasting by Satellite) standard, which is also well known in the art (ETS 300 421). An MPEG2 transport packet comprises 4 header bytes, 184 payload bytes and optionally 16 redundant bytes for an error correcting code. The transport packets are transmitted on an uplink frequency channel.
In the transmitters of the above system the allocation of uplink frequency channels is fixed or virtually fixed. Onboard the satellite, channels are then selected by filtering using passive components; this filtering is therefore fixed. The multiplexing providing the transmit multiplex is sequential; it is therefore also fixed. A bundle of programs is therefore defined only by allocating frequency channels to the transmitters supplying the programs constituting the bundle of programs.
The drawback of a system of the above kind is that the television program broadcast operator is dependent on the program sources and the transmitters for composing its bundle of programs. This is inflexible and gives rise to additional operating costs.
A similar problem arises with service and information data (SI data), also defined by the standard mentioned above, and part of which comprises data transmitted to users to enable them to exploit the transmit multiplex. Of course, SI data of the above kind can be combined in a station and supplied to a transmitter as a particular program to be broadcast. This requires dedicated resources, in addition to program control resources, which represents additional constraints and costs that it would be desirable to limit.
The invention provides a simpler and less costly solution to these problems.
The satellite communication system in accordance with the invention for broadcasting audiovisual programs and multimedia data comprises:
in at least two ground stations, means for transmitting programs to a satellite, each program being transmitted on an uplink frequency channel,
on a satellite, program multiplexing means receiving at least two of said programs and routing them onto a single downlink frequency channel,
in a configuration station on the ground, system data transmission means, said data being transmitted on at least one uplink frequency channel,
onboard the satellite, means for receiving such system data associated with said at least one uplink frequency channel, and
onboard the satellite, configuration means for selectively associating uplink frequency channels and one downlink frequency channel in response to at least some of said system data received by said receive means, the latter data constituting configuration data.
In one embodiment said system data is transmitted in the form of a program dedicated to that purpose and thus inserted into an uplink frequency channel dedicated to that program.
In one embodiment of the invention said configuration means comprise means for selecting said received configuration data and configuration control means for determining accordingly to use the received configuration.
If said configuration means essentially comprise a multiplexer for multiplexing transport packets from a plurality of uplink frequency channels, said control means determine the identities of frequency channels of which said multiplexer receives transport packets for multiplexing them on said downlink frequency channel.
According to another feature, said system data comprises service information data retransmitted by the satellite on said downlink frequency channel.
The communication system according to the invention further comprises a service information processor receiving the service information of programs constituting a bundle of programs and compiling said information to constitute program bundle service information which is inserted into a program on said downlink frequency channel.
In one embodiment said service information processor is coupled to an uplink frequency channel to receive thereon configuration information determining the conditions of said compilation of service information.
In one embodiment said service information processor is connected to said downlink frequency channel by extractor means extracting service information packets relating to the programs and replacing them as required with stuffing packets.